This disclosure relates to reducing noise in images reconstructed from data acquired during an examination of an object via ionizing radiation, such as x-rays or gamma rays. It finds particular application in medical environments where dosage to a patient is monitored, however it may also find applicability in security, industrial, and/or other applications where noise reduction in reconstructed images is desirable.
Today, radiation imaging systems such as computed tomography (CT) systems, single-photon emission computed tomography (SPECT) systems, digital projection systems, and/or line-scan systems, for example, are useful to provide information, or images, of interior aspects of an object under examination. The object is exposed to rays of radiation photons (e.g., x-ray photons, gamma ray photons, etc.) and radiation photons traversing the object are detected by a detector array positioned substantially diametrically opposite a radiation source relative to the object. A degree to which the radiation photons are attenuated by the object (e.g., absorbed, reflected, etc.) is measured to determine one or more properties of the object, or rather aspects of the object. For example, highly dense aspects of the object typically attenuate more radiation than less dense aspects, and thus an aspect having a higher density, such as a bone or metal, for example, may be apparent when surrounded by less dense aspects, such as tissue or clothing.
Noise is inherently introduced into the system when measuring or sampling photons or rather when measuring/sampling charge generated from photons impinging the detector array. This noise is sometimes referred to as photon noise, and artifacts (e.g., streaking, blurring, etc.) in images generated from an examination are sometimes attributable, at least in part, to this photon noise. Accordingly, the photon noise may reduce the quality of an image.
Due to quantum statistics, the photon noise level (e.g., ratio of photon noise to useful signal) generated from an examination of an object is inversely related to the dose of radiation applied to the object. For example, the photon noise level increases as the dose applied to the object decreases. Accordingly, in some applications, the dose of radiation applied to the object is balanced with the desire for images having few to no artifacts.